Oil well scraping device

ABSTRACT

An oil well scraping device includes an integral central mandrel with tapered grooves about its periphery slidably holding scrapers which extend radially beyond the periphery of the central mandrel. An adjustable collar is threaded to the mandrel and serves as a stop for the upper ends of the scrapers so that by adjustment of the axial position of the adjustable collar, the position of the scrapers in the tapered grooves is adjusted to a positive setting which in turn determines their minimum radial extent. This radial extent defines an internal diameter of clearing of a borehole of scale and the like. The scrapers are individually spring loaded to extend beyond the positive setting by the adjustable collar so that continuous engagement of the scrapers with the borehole side walls will take place. Two sets of grooves and scrapers are provided separated by a spacing collar and staggered circumferentially relative to each other to assure three hundred sixty degree scraping action on the borehole side walls.

United States Patent [1 1 Hammon et al.

[ 1 Sept. 11, 1973 [63] Continuation-in-part of Ser. No. 214,697, Jan. 3,

1972, abandoned.

[52] US. Cl. 166/173 [51] Int. Cl 12216 37/02 ['58] Field of Search 166/170-177 [56] References Cited UNITED STATES PATENTS 2,203,966 6/1940 Otis 166/174 2,464,390 3/1949 Hammer 166/173 2,693,239 11/1954 Emanuel 166/173 3,032,114 5/1962 Best 166/173 3,326,294 6/1967 Neilson 166/173 3,251,418 5/1966 Condra.....'. .1 166/174 X 3,105,555 10/1963 Villalon 166/175 X OIL WELL SCRAPING DEVICE Inventors: Donald P. Hammon, Long Beach,

Calif.; Edwin J. Hammon, Albuquerque, N. Mex.

Assignee: Industrial Concepts Corp., Albuquerque, N. Mex.

Filed: Feb. 12, 1973 Appl. No.: 331,381

Related US. Application Data Primary Examiner-David H. Brown Attorney-Pastoriza & Kelly [57] ABSTRACT An oil well scraping device includes an integral central mandrel with tapered grooves about its periphery slidably holding scrapers which extend radially beyond the periphery of the central mandrel. An adjustable collar is threaded to the mandrel and serves as a stop for the upper ends of the scrapers so that by adjustment of the axial position of the adjustable collar, the position of the scrapers in the tapered grooves is adjusted to a positive setting which in turn determines their minimum radial extent. This radial extent defines an internal diameter of clearing ofa borehole of scale and the like. The scrapers are individually spring loaded to extend beyond the positive setting by the adjustable collar so that continuous engagement of the scrapers with the borehole side walls will take place. Two sets of grooves and scrapers are provided separated by a spacing collar and staggered circumferentially relative to each other to assure three hundred sixty degree scraping action on the borehole side walls.

ll Claims, 5 Drawing Figures on. WELL SCRAPING DEVICE BACKGROUND OF THE INVENTION Scraping devices for oil well boreholes are already known in the art and generally comprise a mandrel with radially extending shoes or scrapers which serve to clear a borehole upon lowering of the mandrel into the borehole. The radial extent of the shoes determines the cleared inside diameter of the borehole and in many instances this radial extent is determined by the physical size of the shoe or scraper device; that is, the amount it extends radially beyong the periphery of the mandrel. In some instances, springs have been provided biasing the scrapers in a radially outward direction.

More advanced designs for scrapers contemplate the provision of camming surfaces on the exterior of the mandrel against which thescrapers bear, the position of the scraper along the camming surface determining its radial extent. With this type of structure, the degree of radial extent can be adjusted without having to physically change the scrapers themselves. On the other hand, such arrangements of the camming type as have been proposed are subject to damage to the scrapers or possibly working loose of the scrapers from the mandrel itself. The problem is particularly aggravated if the scrapers become stuck in the borehole and it is attempted to loosen them. In addition, many scraping devices known are solid and thus circulation cannot be maintained during a scraping operation. There thus results the necessity of flushing out the borehole at intermediate periods all resulting in lost time and expense.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention contemplates an improved scraping device wherein many of the disadvantages of prior art devices are overcome.

More particularly, the present invention provides a central mandrel having a plurality of grooves tapering in length in its exterior side walls running parallel to the axis of the mandrel and spaced circumferentially from each other about the periphery of the mandrel. Scraper means in turn are slidable' in an axial direction in the grooves, the floor of the grooves sloping radially inwardly to define the taper of the grooves so that the axial position of the scraper means in the grooves determ ines their radial extent beyond the periphery of the mandrel. An adjustable collar is threaded exteriorly onto the mandrel and axially adjustable along the mandrel to function as a stop against axial movement of the scraper means after an adjusted axial position of the adjustable collar relative to the grooves has been made. Biasing means on the mandrel may be provided to urge the scrapers in a direction against the adjustable collar. The minimum radial extent ofthe scraper means is adjustable by adjusting the threaded position of the adjustable collar.

An important feature of this invention resides in the provision of spring means associated with each scraper means urging the scrapers radially outwardly from the floor of the grooves so that they are at all times in engagement with the borehole side walls. On the other hand, the axial position of the scraper means in the grooves determines a positive point of seating of the scraper means to thereby define a minimum cleared inside diameter of the borehole. As stated, this minimum diameter to be cleared is adjustable by the adjustable collar on the mandrel. Thus, both functions of gauging and scraping can be carried out with a single run into the borehole.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention will be had by now referring to the accompanying drawings in which:

FIG. 1 is a cross-section of a typical oil well borehole to be scraped and gauged by the scraping device of the present invention, the latter device being shown in full lines inserted in an oil well pipe string;

FIG. 2 is an enlarged longitudinal cross-section of the scraping device of FIG. 1;

FIG. 3 is a transverse cross-section taken in the direction of the arrows 3-3 of FIG. 2;

FIG. 4 is an exploded fragmentary perspective view of a portion of the scraping device useful in describing certain details; and

FIG. 5 shows a modified form of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1 there is shown an oil well borehole 10 including a casing 11 which it is desired to scrape. In this respect, scale, debris, and other foreign material can build up on the casing wall. In addition, irregularities in the internal diameter can result from perforating operations. In any event, it is desirable to clear the borehole to a given minimum inside diameter and simultaneously scrape the same.

In accord with the present invention, a scraping operation will function to clear the borehole positively to such given minimum diameter. The scraping device itself for this purpose is indicated generally by the numeral l2 and is arranged to be inserted in a drill pipe string between two of the pipes such as indicated at 13 at the upper end and at 14 at the lower end.

The scraping device 12 itself includes a central mandrel 15, an adjustable collar 16, a spacing collar 17, and upper and lowersets of scrapers 18 and 19. Optionally, a compression spring 20 may encircle the lower portion of the mandrel l5 and bear against a seating ring 21 engaging the lower ends of the lower set of scrapers 19 as shown. The other end of the compression spring 20 is .secured to the mandrel in a set axial position by a stop ring 22.

The adjustable collar 16 is threaded to exterior threads 23 on the mandrel 15 such that rotation of the collar will move it axially up and down the mandrel. By using the compression spring 20, it will be evident that adjustment of the adjustable collar 16; for example, to a higher axial position, will result in the spring urging the upper set of scrapers l8, spacing collar 17, and lower set of scrapers 19 all axially upwardly.

Referring now to FIG. 2 further details of the scraping device will be evident. As shown, the central mandrel 15 is of an integral construction and includes a central passage 24. The opposite ends of the mandrel are threaded as at 15a and 15b for direct connection in an oil pipe string as described in FIG. 1. With this arrangement, circulation can be maintained through the pipe string and mandrel during a scraping operation.

The internal threading of the adjustable collar 16 to the external threads 23 is evident in FIG. 2. Preferably, this threading is relatively fine with a small pitch so that very minute adjustments can be made in the vertical positioning of the adjustable collar 16 relative to the mandrel. It will be understood, of course, that the spacing collar 17 simply surrounds the mandrel and is slidably vertically therealong and by means of the compression spring 20 it is urged through the lower set of scrapers 19 in an upward direction to sandwich the upper set of scrapers 18 between itself and the adjustable collar 16.

Still referring to the central mandrel 15 of FIG. 2, it will be noted that this mandrel has an upper set of tapered grooves on its exterior wall running in the axial direction of the mandrel and circumferentially spaced. Also provided is a lower set of tapered grooves 26 on the exterior wall of the mandrel running in the axial direction of the mandrel and axially spaced below the upper set. This lower set is alsocircumferentially spaced in a staggered relation with respect to the upper set. The lower set of grooves 26 is indicated by the dotted lines in FIG. 2.

In the preferred embodiment of the invention, there are provided four tapered grooves in the upper set and four tapered grooves in the lower set, the grooves in each set being circumferentially spaced ninety degrees from each other and the grooves in the lower set being staggered relative to the upper set by a circumferential distance of 45. It will be noted that each of the grooves includes a floor which is shallow at its upper end and deeper at its lower end; that is, the floor of the groove extends further radially inwardly at its lower end than at its upper end.

Referring to FIG. 3, the four upper set of grooves will be evident with a corresponding number of scrapers 18 slidably received therein. The lower scrapers 19 are depicted by the dotted lines and the staggered or circumferentially displaced position thereof will be evident. The circumferential extent of the surface of the scraper is indicated by the letter C and this circumferential extent is designed tov be greater than 45. Thus, it is assured that the inside borehole walls are engaged over a complete 360 when both sets of scrapers are arranged as shown.

Referring now to FIG. 4, details of the scraper and groove structure will be evident. Since the grooves and scrapers are all identical, a detailed description of one will suffice for all. As will be clear from FIG. 4, the floor of the tapered groove 25 slopes downwardly so that it is shallowest at its upper end and deepest at its lower end. The depth is indicated by the small letter d and the overall axial length of the groove is indicated by the letter L. The side walls of the groove are undercut as at 27 over a major portion of their length L.

Referring now to the scraper 18, it will be noted that this member includes a foot portion 28 including outwardly extending flanges 29. These flanges 29 are arranged to be received under the under-cut portions 27 of the groove when the scraper is slid into the groove so that the scraper is keyed in the groove. In this regard, the upper portions of the groove side walls are relieved as at 30; that is, they are not under-cut so that it is a simple matter to slide the scraper 18 into and out of the groove from the upper ends of the grooves.

The bottom of the foot portion 28 includes small bores 31 for receivng small coiled springs 32. These springs 32 will engage the floor of the groove 25 thereby biasing the flanges 29 against the underside of the undercut edges 27 of the groove side walls. However, the small bores 31 accomodating the coil springs 32 are sufficiently deep that the bottom of the foot portion 28 can seat solidly on the floor of the groove 25, when urged inwardly.

FIG. 5 shows a modified form of the scraper tool which is the same in all respects to the tool described in FIGS. 1 through 4 with the exception that the large helical spring 20 shown in FIG. 2 is eliminated. Thus, referring to FIG. 5 the modified tool is shown in the borehole 10 for scraping the casing 11. As in the embodiment of FIGS. 1 through 4, the tool comprises a central mandrel 33 with a fine threaded portion 34 and threaded collar 35. A first set of four scrapers 36 is shown together with the spacer collar 37 and a second lower set of scrapers 38. Each of the scrapers is spring loaded radially outwardly and keyed in a tapered groove such as indicated at 39 all as described in FIGS. 3 and 4.

Ratherthan the helical spring 22, the lower portion of the mandrel is threaded at 40 and provided with a threaded stop collar 41. 1

Since each of the scrapers is biased radially outwardly in its keyed groove, it will be held by friction in a set axial position along the groove without the need of the coiled helical spring to urge the same in an upward direction, Further, it will be evident that as the mandrel is lowered in the borehole and the scrapers engage the borehole side walls, the friction drag will urge them upwardly against the lower end of the spacing collar 37 and the lower end of the adjustable collar 35 so that in the borehole they will be in their uppermost axial position as determined by the position of the adjustable collar 35.

OPERATION The scraper devices described in'FIGS. 1 through 5 can be easily assembled. When the compression spring 20 isused, it is initially positioned over the mandrel 15 to seat on the stop ring 22. The seating ring 21 is then inserted over the mandrel to rest on the upper ends of the coiled spring 20. The various scrapers 18 and 19 may then be slid into the tapered grooves of the mandrel at the upper ends of the grooves as described in conjunction withFIG. 4. The lower set of scrapers 19 is first inserted and the spacing collar 17 then received over the upper end of the mandrel 15 and urged downwardly to assure that the scrapers 19 are received well within the groves, this action compressing the compression spring 20. The upper set of scrapers 18 can then be inserted in the upper set of grooves and thereafter the adjustable collar 16 is threaded down on the external threads 23 thereby holding the assembly together.

It will be evident from the foregoing that the scrapers 18 of the upper and lower sets can move downwardly relative to the mandrel 15 by simply compressing the compression spring 20 whereas their upward movement is positively checked by the adjusted position of the adjustable collar 16 on the threads 23. It will therefore be evident that by rotating the collar 16, the axial position of the scrapers 18 and 19 in the respective sets of grooves can be adjusted. Since the floor of the grooves slope as described, the axial positioning of the scrapers will determine their minimum radial extent beyond the periphery of the mandrel 15.

In using the scraping device, the minimum radial extent of the scrapers 18 and 19 is initially adjusted by threading of the adjustable collar 16 to define a given minimum internal diameter of a borehole to be cleared. The mandrel is then inserted in a drill pipe string and the entire string lowered into the borehole. The small coil springs described in FIG. 4 will normally bias the scrapers l8 and 19 radially outwardly away from the sloping floors of the grooves so that they will at all times engage the borehole side walls and remove loose scale and the like. If there is an obstruction which is less than the desired internal diameter to be cleared, the scrapers will seat solidly on the floor of the tapered grooves and thus forced movement of the scraping device past such obstruction will clear the obstruction of the set minimum diameter.

Should the device become stuck in the borehole, pulling up on the drill pipe string will reposition the tapered grooves relative to the struck scrapers l8 and 19 such that a deeper portion of the groove is available to receive the scrapers and radial movement inwardly of the scrapers can take place so that they can be free from their stuck position.

Since the mandrel l5 is hollow, as stated, it will be clear that circulation can be maintained during a scrap ing operation.

If it is desired to change the internal diameter to be cleared in the borehole, it is a simple matter to readjust the adjustable collar 16. For example, if the internal diameter is to be increased, the collar 16 is threaded back up on the threads 23 thereby permitting the scrapers to be raised so that they will seat on a shallower portion of the floor of the grooves when a restricted area is encountered and thus gauge the hole to a greater diameter.

To replace a scraper or to insert new scrapers, it is an easy matter to simply completely'back off the adjustable collar 16 and slide the various scrapers from the grooves, in otherwords, a reverse operation to that of assembling the device takes place.

In the modified scraping device of FIG. 5, the assembly of the scrapers, spacing collar and adjusting collar are the same as described heretofore. The stop collar 41, which is really not essential, is nevertheless provided and can be axially adjusted by threading on the threads 40 to a position such that its upper portion will eclipse exposed portions of the tapered grooves, such exposed portions being indicated at 39. Depending upon the particular setting of the adjustable collar 35, the stop collar 41 is adjusted to leave a small clearance indicated by the letter d below the lower sets of scrapers 38. This small clearance permits the scrapers to be relieved by upward pulling on the mandrel should the scrapers become stuck in a restricted area.

As described heretofore, since the scrapers are individually biased radially outwardly by the coiled springs, they will be held in the grooves in any set position by friction. Further, when lowering the mandrel in the borehole, the continuous engagement of the scrapers with the borehole side walls results in a drag on the scrapers which urges them upwardly against the spacing collar 37 and adjustable collar 35 so that they assume their proper positions notwithstanding the lack of a large coiled spring such as 20 described in FIG. 2.

The advantage of the construction of FIG. 5 resides in the elimination of the large coiled spring which can become damaged or lost in the borehole. Thus the embodiment of FIG. 5 provides a more rugged tool. As mentioned, the stop collar 41 minimizes possible clogging of the grooves by debris in the borehole. It can be set in any position to adjust the distance d and thus ad just the amount of relief deemed necessary to permit the scrapers to retract inwardly upon upward pulling of the mandrel in the event they become stuck. However, it is to be understood that the entire scraping device will function in the absence of the collar 41; in other words, simply removing the coil spring 20 of the embodiment of FIG. 2 will not impair the operation of the scraper.

Summarizing, there are three distinct important features of the scraping device of this invention. First,a

positive inside diameter of a borehole to be cleared can easily be set. In fact, this setting can be set to the thousandths of an inch simply by providing a sufficiently fine micrometer type screw adjustment for the threads 23 in FIG. 2 or the threads 34 in FIG. 5. Second, the scraper blades are spring loaded beyond the positive setting of the adjustable collar 16 so that they will help in removing looser type scale by always being in engagement with the borehole side walls. This structure results from the small coil springs 32 on the bottom of the foot portion of each scraper. Third, should the scrapers themselves become stuck in any manner, it is a simple matter to pull up on the mandrel which will permit the scrapers to retract radially inwardly and thus easily be freed. v

In addition to the foregoing three basic features, the provision of four scraper blades arranged in an upper set and a lower set circumferentially staggered as described assures that three hundred sixty degree engagement with the borehole walls will take place. This engagement results regardless of the particular setting of positive seating of the scrapers. Thus, a larger variation of the particular setting for given sized scrapers is possible as compared to prior devices which might only provide the three scrapers spaced at This larger variation is possible because a greater retraction and extension of two sets of four scrapers staggered relative to each other while still maintaining 360 engagement can be made as compared to two sets of three scrapers stag gere d relative to each other.

Some still further features are evident from the described embodiments. First, the one piece construction for the central mandrel provides for great strength and economy in the manufacture of the tool. In addition, by providing the tapered grooves, the scrapers are stabilized laterally by the edges of the grooves. This construction has the advantage that the mandrel can be rotated without dislodging the scrapers as compared to a simply gradually reduced diameter portion of the mandrel over 360 to provide a camming surface. Finally, the provision of scrapers which are spring loaded radially outwardly enables the large coiled spring 22 to be eliminated since the action of the small spring biasing the scrapers radially outwardly against the borehole side walls will result in the scrapers being held by teh side-walls as the mandrel is lowered until they engage the adjustable collar, continued downward movement of the mandrel keeping the scrapers in their set positions.

A major advantage of the scraping tool of the present invention is the fact that a borehole may be gauged to a given set minimum diameter and simultaneously scraped so thattwo operations are carried out with one 'clear the borehole of scale and the like, comprising, in

combination:

a. a central mandrel having a plurality of grooves tapering in depth inits exterior side walls running parallel to the axis of the mandrel and spaced circumferentially from each other about the periphery of the mandrel;

b. scraper means slidable in an axial direction in said grooves, the floor of the grooves sloping radially inwardly to define the taper of the grooves so that the axial position of the scraper means in the grooves determines their minimum radial extent beyond the periphery of said mandrel; and

. an adjustable collar threaded exteriorly onto said mandrel and axially adjustable along the mandrel to function as a stop against axial movement of the scraper means after an adjusted axial position of the adjustable collar relative to the groove has been made,

whereby the minimum radial extent of the scraper means is adjustable by adjusting the threaded position of .the adjustable collar; each of the scraper means being spring-loaded in a radial outward direction so that a continuous engagement of the borehole side wall by the scraper means will take place and yet positive seating of the scraper means on the floor of the grooves determines a minimum diameter for the borehole which is cleared.

2. A scraping device according to claim 1, in which said mandrel has a central passage and is threaded at its ends for insertion in an oil pipe string whereby circulation can be maintained while scraping an oil well borehole.

3. A scraping device according to claim 2, in which the sloping floor of each of the grooves is shallow at its upper end and deepest at its lower end, said adjustable collar being disposed above the scraper means to act as a check against upward movement of the scraper means during a scraping operation when lowering the pipe string in the borehole, upward movement of the pipe string loosening any sticking of the scraper means to the borehole side walls as a consequence of the deeper portions of the grooves being positioned to accommodate radial inward movement of the scraper means.

4. A scraping device according to claim 3, in which each of the scraper means is keyed into its associated groove against completely outward radial movement of the scraper means to a point where it is free of the grooves along a major portion of the grooves, an end portion of the grooves being free of the keying of the scraper means so that they may he slid free of the grooves by backing off the adjustable collar.

5. A scraping device for passing along a borehole to clear the borehole of scale and the like and to define 'a given inside minimum diameter for the borehole,

comprising, in combination:

a. a central mandrel having an upper set of tapered grooves on its exterior wall running in the axial direction of the mandrel and circumferentially spaced and a lower set of tapered grooves on its exterior wall running in the axial direction of the mandrel and axially spaced below said upper set and circumferentially spaced with respect to said upper set, each of the tapered grooves having a sloping floor defining a shallow upper end and a deeper lower end, the edges of the side walls of the grooves being undercut along a major portion of their lengths;

b. an adjustable collar surrounding said mandrel above the lower ends of said upper set of grooves and being'threadedly engaged with said mandrel so that said collar is movable axially along said mandrel by rotating the collar;

c. an upper set of scrapers slidable in said upper grooves along the sloping floors thereof respectively such that their minimum radial extent from said mandrel is determined by their axial positions in the upper grooves;

d. a lower set of scrapers slidable in said lower grooves along the floors thereof respectively such that their minimum radial extent from said mandrel is determined by their axial positions in the lower grooves each of the upper and lower scrapers having a foot portion with laterally extending flanges receivable in the under-cut portions of the side walls of the groove to hold the scraper in the groove; I

. a spacing collar surrounding said mandrel between the upper and lower sets of scrapers and axially movable along said mandrel; and

means biasing the scrapers radially outwardly away from the floor of the groove so that the flanges engage under the under-cut portion to hold the scraper in a set axial position, whereby the threaded axial position of said adjustable collar determines the position of the scrapers along the grooves so that a positive setting of the adjustable collar defines a given minimum radial extent of the scrapers to define said given inside minimum diameter, readjustment of said adjustable collar changing the minimum radial extent of the scrapers so that a different inside diameter may be cleared in the borehole.

6. A scrapingdevice according to claim 5, in which said-central mandrel includes a center passage and threaded upper and lower ends for insertion in an oil pipe strong so that said scraping device can be used to scrape an oil well borehole while maintaining circulation through the well pipe string.

7. A scraping device according to claim 5, in which said means biasing the scrapers radially outwardly includes spring means on the foot of each scraper engaging the floor of the groove to bias the scraper outwardly.

8. A scraping device according to claim 5, in which the under-cut portions of the groove walls terminate at the upper shallow end of the groove so that the scrapers may be slid out of their grooves by backing off the adjustable collar and spacing collar to facilitate the replacement of said scrapers.

9. A scraping device according to claim 5, in which there are provided four grooves in the upper set and four grooves in the lower set circumferentially spaced at ninety degrees to each other respectively, the staggering of the lower set being such that the lower set is circumferentially spaced 45 from the upper set, and in which each of said scrapers has a scraping surface extending over a given circumferential distance greater than 45 to that engagement of the borehole side walls by the scrapers total a complete 360, the upper set of scrapers engaging portions of the borehole side wall missed by the lower set of scrapers.

10. A scraping device according to claim including a stop collar threaded onto the lower end of said mandrel below said lower set of scrapers so that lower exposed portions of said lower set of tapered grooves may be partially eclipsed by the upper portion of said stop collar. 

1. A scraping device for passing along a borehole to clear the borehole of scale and the like, comprising, in combination: a. a central mandrel having a plurality of grooves tapering in depth in its exterior side walls running parallel to the axis of the mandrel and spaced circumferentially from each other about the periphery of the mandrel; b. scraper means slidable in an axial direction in said grooves, the floor of the grooves sloping radially inwardly to define the taper of the grooves so that the axial position of the scraper means in the grooves determines their minimum radial extent beyond the periphery of said mandrel; and c. an adjustable collar threaded exteriorly onto said mandrel and axially adjustable along the mandrel to function as a stop against axial movement of the scraper means after an adjusted axial position of the adjustable collar relative to the groove has been made, whereby the minimum radial extent of the scraper means is adjustable by adjusting the threaded position of the adjustable collar; each of the scraper means being spring-loaded in a radial outward direction so that a continuous engagement of the borehole side wall by the scraper means will take place and yet positive seating of the scraper means on the floor of the grooves determines a minimum diameter for the borehole which is cleared.
 2. A scraping device according to claim 1, in which said mandrel has a central passage and is threaded at its ends for insertion in an oil pipe string whereby circulation can be maintained while scraping an oil well borehole.
 3. A scraping device according to claim 2, in which the sloping floor of each of the grooves is shallow at its upper end and deepest at its lower end, said adjustable collar being disposed above the scraper means to act as a check against upward movement of the scraper means during a scraping operation when lowering the pipe string in the borehole, upward movement of the pipe string loosening any sticking of the scraper means to the borehole side walls as a consequence of the deeper portions of the grooves being positioned to accommodate radial inward movement of the scraper means.
 4. A scraping device according to claim 3, in which each of the scraper means is keyed into its associated groove against completely outward radial movement of the scraper means to a point where it is free of the grooves along a major portion of the grooves, an end portion of the grooves being free of the keying of the scraper means so that they may be slid free of the grooves by backing off the adjustable collar.
 5. A scraping device for passing along a borehole to clear the borehole of scale and the like and to define a given inside minimum diameter for the borehole, comprising, in combination: a. a central mandrel having an upper set of tapered grooves on its exterior wall running in the axial direction of the mandrel and circumferentially spaced and a lower set of tapered grooves on its exterior wall running in the axial direction of the mandrel and axially spaced below said upper set and circumferentially spaced with respect to said upper set, each of the tapered grooves having a sloping floor defining a shallow upper end and a deeper lower end, the edges of the side walls of the grooves being undercut along a major portion of their lengths; b. an adjustable collar surrounding said mandrel above the lower ends of said upper set of grooves and being threadedly engaged with said mandrel so that said collar is movable axially along said mandrel by rotating the collar; c. an upper set of scrapers slidable in said upper grooves along the sloping floors thereof respectively such that their minimum radial extent from said mandrel is determined by their axial positions in the upper grooves; d. a lower set of scrapers slidable in said lower grooves along the floors thereof respectively such that their minimum radial extent from said mandrel is determined by their axial positions in the lower grooves each of the upper and lower scrapers having a foot portion with laterally extending flanges receivable in the under-cut portions of the side walls of the groove to hold the scraper in the groove; e. a spacing collar surrounding said mandrel between the upper and lower sets of scrapers and axially movable along said mandrel; and f. means biasing the scrapers radially outwardly away from the floor of the groove so that the flanges engage under the under-cut portion to hold the scraper in a set axial position, whereby the threaded axial position of said adjustable collar determines the position of the scrapers along the grooves so that a positive setting of the adjustable collar defines a given minimum radial extent of the scrapers to define said given inside minimum diameter, readjustment of said adjustable collar changing the minimum radial extent of the scrapers so that a different inside diameter may be cleared in the borehole.
 6. A scraping device according to claim 5, in which said central mandrel includes a center passage and threaded upper and lower ends for insertion in an oil pipe strong so that said scraping device can be used to scrape an oil well borehole while maintaining circulation through the well pipe string.
 7. A scraping device according to claim 5, in which said means biasing the scrapers radially outwardly inCludes spring means on the foot of each scraper engaging the floor of the groove to bias the scraper outwardly.
 8. A scraping device according to claim 5, in which the under-cut portions of the groove walls terminate at the upper shallow end of the groove so that the scrapers may be slid out of their grooves by backing off the adjustable collar and spacing collar to facilitate the replacement of said scrapers.
 9. A scraping device according to claim 5, in which there are provided four grooves in the upper set and four grooves in the lower set circumferentially spaced at ninety degrees to each other respectively, the staggering of the lower set being such that the lower set is circumferentially spaced 45* from the upper set, and in which each of said scrapers has a scraping surface extending over a given circumferential distance greater than 45* to that engagement of the borehole side walls by the scrapers total a complete 360*, the upper set of scrapers engaging portions of the borehole side wall missed by the lower set of scrapers.
 10. A scraping device according to claim 5 including spring means on the mandrel bearing against the lower ends of the lower set of scrapers to exert an upward axial force thereon said force being transmitted through said spacing collar to the upper set of scrapers to sandwich the upper scrapers between said spacing collar and adjustable collar.
 11. A scraping device according to claim 5, including a stop collar threaded onto the lower end of said mandrel below said lower set of scrapers so that lower exposed portions of said lower set of tapered grooves may be partially eclipsed by the upper portion of said stop collar. 